Children born with a single functional ventricle face inordinate challenges over the entirety of their lives. A multiple staged operative treatment strategy offers hope for survival—at high physiologic, financial, and societal cost. Those who are fortunate to survive typically endure lengthy and complex hospital courses. Pathophysiology induced at each stage impacts not only the timing, course, and outcome of subsequent surgical stages, but also impacts long-term status. The staged surgical paradigm has evolved on a clinical basis, and is putatively the only reasonable approach. Because of this, alternative paths to achieve the same result have been neither evident nor sought. There may, in fact, be a safer and more sensible approach.
In a univentricular Fontan circulation, there is no subpulmonary ventricular power source to pump systemic venous blood through the lungs. Consequently, systemic venous pressure is significantly elevated and cardiac output is suboptimal. One way to address such problems includes a means to gently augment blood flow from the great veins through the lungs which would reduce venous pressure and improve ventricular filling, creating conditions comparable to a normal two-ventricle circulation. A gradual reduction in support would allow for a stable transition to elevated systemic venous pressure. Once the circulation has adapted to permit a systemic venous source to perfuse the lungs at normotensive pressures, support can be safely withdrawn.
The treatment of single ventricle heart disease is a highly complex and formidable challenge. It is the fifth most common heart defect, and is the leading cause of death from all structural birth defects in the first year of life. It is also the most costly to treat. Affected infants are typically otherwise normal. Only 50-70% survive through all 3 staged procedures. Fontan repair of single ventricle is considered long-term palliation, and represents a transition from acute to chronic disease. At best, children are left with the physiologic limitations inherent in a univentricular circulation. Despite medical and surgical advances, improved outcomes using the staged protocol have not been realized. Furthermore, for older patients with failing Fontan physiology, therapies are limited: medical therapy indirectly addresses secondary sequelae, and heart transplantation is an end-stage option. One million American adults are now alive with congenital heart disease; those with single ventricle physiology (SVP) represent a significant percentage and are the most problematic subgroup. They utilize resources disproportionate to their numbers, constituting an emerging public health concern. The NHLBI Working Group in Research in Adult Congenital Heart Disease has called for mechanistic and bioengineering research to improve the care of the growing number of children and adults surviving with SVP.
Patients with a univentricular Fontan circulation are at high risk of circulatory insufficiency not only at the time of repair, but also as they age. This is presumably due to the combined sequelae of elevated systemic venous pressure, reduced preload to the single ventricle, and increased afterload. A blood pump specifically designed to augment cavopulmonary flow would address these problems and improve circulatory status by producing conditions more similar to the normal two-ventricle circulation. This is supported by the clinical improvement observed in patients who undergo Fontan conversion from atriopulmonary to total cavopulmonary connections. Hydraulic efficiency in their cavopulmonary circulation is improved by a seemingly trivial, yet highly significant, 2-5 mmHg, which reduces systemic venous pressure, and improves transpulmonary flow and cardiac output.
Numerical modeling of the flow dynamics in a total cavopulmonary connection has been performed (NIH R01 grant #HL67622). It has been shown that a central diverting body at the TCPC intersection will effectively split incoming vena caval flow toward each of the outlets, reducing turbulent kinetic energy loss and maximizing hydraulic efficiency. However, incorporation of a fixed central diverting body into the venous walls as a permanent flow diversion is surgically impractical: In the low-pressure venous circulation, this may be thrombogenic, and would lack growth potential, precluding consideration in children.
Experimental reports of mechanically assisted neonatal Stage-2 Fontan procedures using a paracorporeal pump are also emerging (Reference a February 2009 publication: Honjo O, Merklinger S L, Poe J B, Guerguerian A M, Algamdhi A A, Takatani S, Van Arsdell G S. Mechanical cavopulmonary assist maintains pulmonary and cerebral blood flow in a piglet model of a bidirectional cavopulmonary shunt with high pulmonary vascular resistance. J Thoracic Cardiovasc Surg 2009; 137:355-61). There is growing awareness of the need for innovative paradigms to treat patients with SVP and this can be achieved by assisting cavopulmonary flow. Awareness is growing that this is a viable and improved approach to solve the problems associated with repair of functional single ventricle.
In addition to the problems faced by children born with a single functional ventricle, related problems are faced by patients with congestive heart failure that need temporary or permanent support of their right ventricular function. In patients with congestive heart failure, the most common cause of right heart failure is left heart failure. Furthermore, right heart failure is typically a recoverable event within a span of 2 weeks once the source of left heart failure is addressed. This short time period of recovery makes clinical decision making to commit the patient to surgically invasive right ventricular assist device (RVAD) support difficult. This is an invasive procedure which carries significant complications in patients who are critically ill at baseline.
The hydraulic needs for right ventricular support are approximately one-fifth of the needs for left ventricle support. Support for the right ventricle, particularly if used non-invasively percutaneously inserted, would be most beneficial in conjunction with traditional mechanical LVAD support in patients in whom biventricular dysfunction is present, and in whom the right ventricular dysfunction is felt to be transient secondary to left heart failure and recoverable. In such cases, an improvement in left heart performance via surgical LVAD support will ultimately result in secondarily improved right heart performance. Only temporary right heart support (estimated at ⅕th the level of systemic or left heart support) may be necessary until right ventricular function has completely recovered, thus solving the current problem of the need to place a highly invasive and permanent device. Reasonably percutaneous temporary RVAD support devices do not currently exist.
In most cases, right heart support is needed only temporarily until the right ventricle regains function. If an invasive procedure can be avoided, the patient will benefit from having a percutaneous device that can be easily removed when no longer needed. Some available percutaneous devices require trans-septal atrial puncture to deliver assisted flow to the left heart, which has several disadvantages: 1) it is technically challenging to puncture the atrial septum and position the large cannulae, and 2) the blood which is delivered to the systemic circulation via the left atrium is deoxygenated, resulting in systemic oxygen desaturation.
The estimated clinical need related to the heart failure market is substantial:                Heart failure affects 10 million people globally (5 million in US), with 1 million new cases diagnosed every year        1 million patients in NYHA Class IV (end-stage) disease        Of these, an estimated 100,000 per year would benefit from the implantation of a heart pump.        In the US, heart failure remains Medicare's greatest area of healthcare-related spending        Long-term device treatment is reimbursed in the US at a minimum USD136,000. Of this, typically USD75,000 is for the device.        A temporary, disposable, right-heart support device would cost less than that for an implantable device, with reduced morbidity and mortality, resulting in a substantial health care cost reduction and societal benefit.        
In addition to the requirements for active assistance of cavopulmonary flow (i.e. components that add energy to the flowing medium), there are also requirements for passive devices (i.e. components that do not add energy, but rather optimize existing flow). As examples, consider the low pressure 3-way “T” (by directional Glenn) and 4-way “+” (total cavopulmonary connection (TCPC)) conditions. In both of these conditions it is possible that flow at the intersection of two flow paths or at the bifurcation of a flow path is excessively turbulent, with a commensurate loss in total kinetic energy for fluid passing through the intersection. In such conditions the insertion of a static device could result in a more stable flow pattern, such that fluid exiting the intersection does so with higher kinetic energy.
A recent NIH Initiative (NHLBI-HV-04-01 Pediatric Circulatory Support) called for development of novel, innovative approaches to circulatory support for children with functional single ventricle using technology that is easy to use, rapidly deployed, with minimal prime volumes, and minimal risk of infection, bleeding or thrombosis. A pump according to one embodiment of the present invention fulfills some or all of the approaches.
Various embodiments of the inventions described herein address some or all of the conditions described above, in both novel and unobvious ways.